Historic and current population levels of the common loon are not well known in Washington, with most of the available information dating from the past 15 years. It is a rare breeder and a common migrant and wintering species within the state. A total of 20 confirmed nest sites are known to have been active for at least one year during the years 1979-1999 in Chelan, Douglas, Ferry, King, Okanogan, and Whatcom counties. The number of confirmed nests during 1990-99 ranged from 8-10 each year, with 9-14 sites surveyed. Nesting at 12 additional sites has been reported but not confirmed.

Common loons once were described as a fairly common breeding species both east and west of the Cascade crest, but likely declined between 1890 and 1925 in much of Washington. Declines across the U.S. during this period are thought to have been the result of shooting. A number of lakes in Washington appear to have offered ideal conditions for loon nesting in the past. Characteristic sites would have been relatively undisturbed forest lakes at least 20 ha (49 ac) in size, with deep inlets and bays. They would have had islands or logs and other floating debris for nest sites. Finally, they would have been characterized by good water quality, an adequate food source, and seclusion from intense human activity. At many lakes, unfortunately, these conditions have been lost.

Shoreline development, including homes, roads, and powerlines, has eliminated nesting habitat and increased the level of human activity in the vicinity of potential loon nests. Human disturbance is likely to reduce loon productivity and may preclude nesting at important sites. Persecution directed toward loons can cause abandonment of nesting sites. Drastic changes in water level (frequent events at reservoirs) either flood nests or render them unapproachable, causing abandonment. Based upon historic records, the species has a reduced opportunity to breed in the Puget Sound region, compared with historic conditions. Loons no longer nest at 4 lakes in western Washington and one lake in eastern Washington where nesting was known early in the 20th century.

Although human influences are problematic, allowances for loons sometimes are made. Floating nest platforms, access restrictions, and educational campaigns have helped loons to persist and successfully reproduce at certain sites. The development of reservoirs on rivers from dam construction has created some nesting and wintering habitat for common loons. Currently, about half the loon nests documented each year are located on water bodies that are relatively inaccessible to people, so they have limited human disturbance.

Increased development and recreational pressure at sensitive nesting lakes must be actively managed to prevent further loss of nesting loons. Protection and education programs must be expanded to appropriate lakes that currently do not support breeding loons to allow the species to recolonize and nest undisturbed, ensuring a stable and well-distributed population. The use of rotenone to kill unwanted fish may affect the food supply of common loons for several years.

The common loon does not merit State Endangered status, because it is not seriously threatened with extinction within the state. It does not appear to merit a State Threatened classification at this time, because we have no evidence of a declining population or a substantial change in distribution. However, because historic records are sketchy and surveys have not been comprehensive, it is not known if the population is stable, increasing or decreasing. Although threats such as human disturbance, predation, and oil spills have been identified, the severity of these threats to the breeding population is not well understood. Numbers of known nests have increased over the past 15 years, but this increase may be a result of increased survey effort. Processes of dispersal and site colonization are also not well understood. New information on these issues may change our understanding of the status of common loons in Washington.

State Sensitive status is warranted because the common loon is a rare breeding species and vulnerable to a number of threats. Loons require special management to breed in proximity to humans, and they are likely to become endangered or threatened without continued cooperative management and removal of threats.

The Department recommends the common loon be classified as a State Sensitive species.